Interactive Self-Study Module: Characteristics of a Boundary Layer over a Flat Surface

Overview:

This module uses a screencast to explain how fluid flows over a flat surface (such as air flowing over the top of a flat roof of a car). Your retention of material in this module will increase if you write down reasons for your answers to ConcepTests and you try to solve the example problems before watching the screencast solutions.
We suggest using the learning resources in the following order:

  1. Attempt to answer the multiple choice ConcepTest and solve the example problem before watching the screencast or working with the simulation.
  2. Watch the screencast that describes boundary layers.
  3. Look over the important equations for shear rates and shear stresses.
  4. Try to solve the example problems before watching the solutions in the screencasts.
  5. Answer the ConcepTests.
  6. Look at the list of key points, but only after you try to list the key points yourself.
Motivation:
  • Before you can understand how a fluid flowing over an object results in a drag force you first need to understand how the fluid interacts with the surface of the object. We will start with a simple case, in which fluid flows over a flat surface.
  • This module is primarily intended for a Fluid Mechanics course. It may also provide a review and background information for convection in a Heat Transfer course.
Before studying this module, you need to:
  • Describe in words and mathematically the meaning of a no-slip boundary condition.
  • Describe in words and mathematically the meanings of a shear rate and a shear stress.
  • By looking at a velocity profile, be able to identify where shear stresses are highest and where they are zero.
  • Review the self-study module, Viscosity and Shear Stress.
After studying this module, you should be able to:
  • Describe in words the velocity profile over a flat surface.
  • Identify where the shear stress is highest and where it is negligibly small for laminar flow over a flat surface.
  • Look at a velocity profile over a flat surface and have a fair understanding of where the boundary layer exists.
  • Make a list of the fluid properties that affect the velocity profile over a flat surface and describe how changes in each property affect the velocity profile and the shape of the boundary layer.